LodePNG decoder
Allow the use of PNG images in LVGL.
Detailed introduction: https://github.com/lvandeve/lodepng
If enabled in lv_conf.h
by LV_USE_LODEPNG
LVGL will register a new
image decoder automatically so PNG files can be directly used as any
other image sources.
- note:
a file system driver needs to be registered to open images from files. Read more about it File system or just enable one in
lv_conf.h
withLV_USE_FS_...
The whole PNG image is decoded, so width x height x 4
bytes free RAM space is required.
The decoded image is stored in RGBA pixel format.
As it might take significant time to decode PNG images LVGL's Image caching feature can be useful.
Compress PNG files
PNG file format supports True color (24/32 bit), and 8-bit palette colors. Usually cliparts, drawings, icons and simple graphics are stored in PNG format, that do not use the whole color space, so it is possible to compress further the image by using 8-bit palette colors, instead of 24/32 bit True color format. Because embedded devices have limited (flash) storage, it is recommended to compress images.
One option is to use a free online PNG compressor site, for example Compress PNG: https://compresspng.com/
Example
Open a PNG image from file and variable
C code
View on GitHub#include "../../lv_examples.h"
#if LV_USE_LODEPNG && LV_USE_IMAGE && LV_BUILD_EXAMPLES
/**
* Open a PNG image from a file and a variable
*/
void lv_example_lodepng_1(void)
{
LV_IMAGE_DECLARE(img_wink_png);
lv_obj_t * img;
img = lv_image_create(lv_screen_active());
lv_image_set_src(img, &img_wink_png);
lv_obj_align(img, LV_ALIGN_LEFT_MID, 20, 0);
img = lv_image_create(lv_screen_active());
/* Assuming a File system is attached to letter 'A'
* E.g. set LV_USE_FS_STDIO 'A' in lv_conf.h */
lv_image_set_src(img, "A:lvgl/examples/libs/lodepng/wink.png");
lv_obj_align(img, LV_ALIGN_RIGHT_MID, -20, 0);
}
#endif